Patients with a history of poliomyelitis may develop new weakness decades after acute infection. The post-polio syndrome (PPS) probably comprises a least 2 clinical entities: a benign treatable myalgic syndrome, and a post-polio progressive muscular atrophy. We hypothesize that very large motor units from the original denervation lose sprouts with time, causing PPMA. We will test the hypothesis by examining the neuromuscular junction of PPMA patients morphologically and neurophysiologically.